Various types of intravascular implants are known including a stent, balloon, cannula, coil, pin and the like. These are employed for treatment of the blood vessel of a person or animal.
Such intravascular implants are required to have various functions and characteristic properties.
For instance, with a stent, such characteristics as mechanical characteristics (high strength, high hardness, high ductility, low recoiling property and the like) and physiological characteristics (prevention of stenosis and restenosis, biodegradability, metal allergy prevention and the like) are required.
For the purpose of meeting these requirements, many studies have been conventionally made with respect to the composition of a material for intravascular implant.
For instance, in Patent Document 1, in order to provide a mechanically and physiologically improved internal artificial organ (stent or the like), there is a description concerning an internal artificial organ of a type having a support structure containing a metal material. The internal artificial organ is characterized in that the metal material includes a magnesium alloy of the following composition: magnesium=>90%, yttrium=3.7% to 5.5%, rare element=1.5% to 4.4%, and residues=<1%.
For the rare earth element, neodymium alone is exemplified.
For the residues, only two elements of zirconium and lithium are exemplified.
In Patent Document 2, for the purpose of providing medical implants (a stent, clip and the like) made of a biodegradable material having mechanical characteristics, there is a description concerning a medical implant, characterized in that the material includes 79 to 97% of magnesium, 2 to 5% of aluminium, 0 to 12% of lithium and 1 to 4% of rare earth elements.
The medical implant can be degraded by corrosion in the living body.
The rare earth elements exemplified include only four elements of cerium, lanthanum, neodymium and praseodymium.
In Patent Document 3, although the invention has its object for providing a medical implant that does not generate a large quantity of gas and is free of heterogeneous decomposition, it is stated that an alloy made of magnesium-gadolinium-yttrium-zinc is a metal material whose corrosion resistance is good.
In Non-patent Document 1, there is described possible induction of restenosis through metal allergies in case where an implant made of a nickel and molybdenum-containing metal material is placed in the living body.    Patent Document 1: Japanese Patent Laid-open No. 2004-160236    Patent Document 2: Japanese Patent Laid-open No. 2001-511049    Patent Document 3: US2004/0241036 A1    Non-patent Document 1: Koster R et. al, “Nickel and molybdenum contact allergies in patients with coronary in-stent restenosis”, The Lancet, England, Elsevier Limited, Dec. 2, 2000, Vol. 356, No. 9245, pp. 1895-1897